aboutToPerformChange

The infrastructure is going to perform the given change. If a
client calls this method it must make sure that the corresponding
method changePerformed(Change) is called after the
change got executed. A typically code snippet looks as follows:

performUndo

query - a proceed query to decide how to proceed if the validation
checking of the undo change to perform returns a non OK status and the
status isn't a fatal error. If null is passed in the
undo proceeds if the status is not a fatal error.

pm - a progress monitor to report progress during performing
the undo change

performRedo

query - a proceed query to decide how to proceed if the validation
checking of the redo change to perform returns a non OK status. If
null is passed in the undo proceeds if the status
is not a fatal error.

pm - a progress monitor to report progress during performing
the redo change